As an example of a process for producing a dispersion of fine water-soluble polymer particles in an aqueous salt solution as dispersion medium having low viscosity and high fluidity in the prior art, processes comprising polymerizing while stirring in the presence of a dispersant such as polymer electrolyte are disclosed in European Patent Publication No. 0183466 and European Patent Publication No. 0364175.
In the case of carrying out the processes disclosed in the patent publications described above, the phenomenon occurs in which the viscosity of the reaction solution increases significantly during polymerization. Consequently, a large load is applied to the agitator, thereby creating the need to use a high-powered motor and stirring blades that are able to withstand high levels of torque. This results in the problem of high cost of the reaction apparatus. In addition, since the viscosity of the reaction solution becomes high, there are portions that are not mixed properly, thereby resulting in the additional problem of the formation of coarse particles.